You are right on 1 of 3 accounts there. The Soviets walked all over JFK, whose foreign policy was a disaster. G.W.Bush watched as the Russians invaded Georgia, as well. Ronaldus Magnus is the only one, out of the three, that verifiable stared down the Russian bear.
Yes, the Russians tried taking the Ukraine under Bush, but here again they withdrew once the Bush Administration made it clear that should they continue, they would be responsible for putting American troops "in harms way" -- something Putin understood as something he did NOT want to force, so Russian troops withdrew.
I think you can successfully argue that the perception that JFK and GW Bush were "weak" in some way which caused the above two events we're discussing, the difference is they quickly squashed that perception and caused our enemy (Russia IS still our enemy) to back down.
Obama can NEVER live down his weakness.